One type of connector system that is small enough to be used in portable cellular telephones, is described in U.S. Pat. No. 5,807,126. That system includes a receptacle that is mounted on a circuit board, with the circuit board having a row of traces. The receptacle has opposite sides that form the upper walls of slots, to position the connector and hold it close to the circuit board. A wall of the receptacle pushes down contacts of the plug against the circuit board traces. One problem encountered with this type of connector results when the cord extending from the plug is pulled up or down. An upward pull on the cord not only tends to lift the mating end of the plug, but also tends to tilt the front end of the plug about a lateral access. This can result in the plug contacts losing engagement with the circuit board traces, and also can result in breakage of the upper slot walls of the receptacle. A downward pull on the cable extending from the plug, can result in opposite tilt of the front end of the plug, which also can cause breakage of the receptacle slot upper wall. Since the receptacle includes a molded plastic body, the receptacle can be strengthened without increasing its size, by using a very high strength engineering plastic, especially one that is filled with glass fibers. However, the strength and rigidity still may not be high enough to avoid contact interruption or breakage in normal use where a pull on the cord of two to five pounds in different directions may be applied. Also, glass fiber reinforced plastics have strengths and rigidities that are not highly consistent. If a receptacle could be further strengthened to resist upward deflection of its slot upper walls, without changing the size of the receptacle, this would result in a small connection system of greater reliability in normal use.